boot-9.scm (read-line): Rewritten to use %read-line.

boot-9.scm (read-line): Rewritten to use %read-line.
ioext.c (%read-line): Return a cons of the input line and its terminator.
fports.c, genio.c, genio.h, ports.c, ports.h: Change fgets methods
	to return the string length as well as its contents.